A typical multi-chip module structure consists of four layers of metal to achieve optimum surface density in the module. Insulated from the substrate is the first or power/ground layer. Extending above the power/ground layer are two layers of metal for electrical signal interconnections. A top or bond pad layer for connecting a die to the substrate extends above the two signal interconnect layers. Historically, to accommodate different applications, each of the four layers of the multi-chip module have been custom designed and fabricated to form the completed module.
Because each layer has to be custom designed and fabricated for each different application, the time and costs incident thereto are considerable. New masks have to be designed for fabricating each separate layer and can not be reused from one application to another. Commercially available anti-fuse programmable modules are process dependent and degrade the density and performance characteristics of the technology.